Topographical models of geographical areas may be used for many applications. For example, topographical models may be used in flight simulators and for planning military missions. Furthermore, topographical models of man-made structures (e.g., cities) may be extremely helpful in applications such as cellular antenna placement, urban planning, disaster preparedness and analysis, and mapping, for example.
Various types and methods for making topographical models are presently being used. One common topographical model is the digital elevation map (DEM). A DEM is a sampled matrix representation of a geographical area which may be generated in an automated fashion by a computer. In a DEM, coordinate points are made to correspond with a height value. DEMs are typically used for modeling terrain where the transitions between different elevations (e.g., valleys, mountains, etc.) are generally smooth from one to a next. That is, DEMs typically model terrain as a plurality of curved surfaces and any discontinuities therebetween are thus “smoothed” over. Thus, in a typical DEM no distinct objects are present on the terrain.
One particularly advantageous 3D site modeling product is RealSite® from the present Assignee Harris Corp. RealSite® may be used to register overlapping images of a geographical area of interest, and extract high resolution DEMs using stereo and nadir view techniques. RealSite® provides a semi-automated process for making three-dimensional (3D) topographical models of geographical areas, including cities, that have accurate textures and structure boundaries. Moreover, RealSite® models are geospatially accurate. That is, the location of any given point within the model corresponds to an actual location in the geographical area with very high accuracy. The data used to generate RealSite® models may include aerial and satellite photography, electro-optical, infrared, and light detection and ranging (LIDAR).
Another advantageous approach for generating 3D site models is set forth in U.S. Pat. No. 6,654,690 to Rahmes et al., which is also assigned to the present Assignee and is hereby incorporated herein in its entirety by reference. This patent discloses an automated method for making a topographical model of an area including terrain and buildings thereon based upon randomly spaced data of elevation versus position. The method includes processing the randomly spaced data to generate gridded data of elevation versus position conforming to a predetermined position grid, processing the gridded data to distinguish building data from terrain data, and performing polygon extraction for the building data to make the topographical model of the area including terrain and buildings thereon.
While it is desirable to process a DEM so that the transitions between terrain, foliage, and cultural features (e.g., buildings) appear as smooth and as seamless as possible, excessive smoothing of a DEM also reduces the accuracy of the features in the image. For example, some of the feature obscurations that my occur include buildings beginning to look like flattened hills, hipped roofs appearing as flat, and trees beginning to look like domes. Moreover, the resolution of DEMs continues to get better, with resolutions of greater than one meter now being possible. Yet, higher resolutions typically result in more noise being present in the image particularly adjacent boundary regions between features, which exacerbates this problem.
Also, it is often desirable to smooth some features but not others. For example, it is desirable to smooth a building roof that appears uneven due to noisy input data. Yet, it is also desirable to maintain the discontinuities of foliage so that it maintains a natural appearance. Accordingly, in certain applications it may be desirable to provide enhanced geospatial model data feature distinguishing and filtering (i.e., smoothing) capabilities.